1. Field
The disclosed embodiments relate to a splice plate for stringers or “stringer splice plate” designed to connect two adjacent stringers. The term “stringer splice plate” is understood to mean a part designed to provide the linkage and alignment of two stringers that are adjacent (i.e. side by side or one in the extension of the other) and the transmission of certain stresses between these two stringers, said stringers being positioned along the longitudinal profile of a structure for which they provide the stiffening. The disclosed embodiments also relate to an orbital joining device designed to fixedly join two adjacent panels of an aircraft fuselage, said orbital joining device comprising at least one stringer splice.
The stringer splice plate according to the disclosed embodiments can be used in all fields where it is required to physically link two adjacent parts so as to maintain the link, alignment and transmission of certain stresses between these two parts.
For example, the stringer splice plate according to the disclosed embodiments can be applied in railroads in order to fixedly join two rails positioned one in the extension of the other, or in aeronautics to fixedly join rails for seats or for all sorts of stiffeners extending along the internal structure of an aircraft.
The orbital joining device of the disclosed embodiments can be applied more particularly in aeronautics. The term “orbital joining” is understood to mean a link between two panels belonging to two adjacent fuselage sections, perpendicularly to the axis of the aircraft.
At present, in aeronautics, there are known ways of connecting two longitudinal stringers positioned one in the extension of the other and facing each other by means of a one-piece stringer splice plate.
2. Description of the Prior Art
In general, and as can be seen in FIGS. 1 and 2 pertaining to the prior art, a cross-piece bar or sleeve is positioned transversely between two panels 1, 2 facing each other on an entire side. The cross-bar 3 is positioned in the zone 4 of attachment between the two panels 1, 2 which do not overlap one another so as to provide for the joining and continuity of the transfer of the stresses and forces along said panels. A vertical frame 5 extends vertically on the collar 3, so as to rigidify the assembly of the link between the two panels 1, 2.
The two stringers 6, 7 facing each other are each fixed to a different panel 1, 2 which they stiffen. In order to maintain the alignment between the two stringers 6, 7, they are linked to each other in a known way by a one-piece stringer splice plate 8, 9.
In FIG. 1 corresponding to the prior art, the one-piece stringer splice plate 8 is fixed by a first extremity 10 to the first stringer 6 and by a second extremity 11, opposite the first end, to the second stringer 7. The body 12 of the stringer splice plate thus connects the two stringers 6, 7 so as to provide longitudinal continuity. Furthermore, the stringer splice plate 8 is fixed to at least two points of the sleeve 3, on either side of the vertical frame 5. Thus, a single-piece unit is fixed to the two stringers 6, 7, the sleeve 3 and the vertical frame 5.
The vertical frame 5 is provided with a vertical notch 13 designed to let through the body 12 of the one-piece stringer splice plate 8. The notch 13 extends vertically along a partial height h of the vertical frame 5, from the base 14 of said vertical frame 5.
FIG. 2 pertaining to the prior art shows another mode of fixation of the two panels 1,2 as currently used in aeronautics, also comprising a sleeve 3 and a vertical frame 5.
The stringer splice plate 9 which connects two adjacent stringers 6, 7 is fixed by a first extremity 15 to the first stringer 6 and by a second extremity 16, opposite the first end, to the second stringer 7. The body 17 of the stringer splice plate extends between the two stringers 6, 7 in the extension of said stringers 6, 7 so as to provide for longitudinal continuity.
In this second embodiment, the vertical frame 5 is clipped above the body 17 of the stringer splice plate 9 so as to preserve its integrity. To this end, vertical plates 18 are positioned on either side of the stringer splice plate and fixedly joined to the sleeve 3 so as to extend vertically relative to said sleeve 3. The vertical frame 5 extends vertically above said vertical plates 18. A top extremity 19 of each plate 18 is fixedly joined to a lower extremity 20 of the vertical frame 5. The body 17 of the stringer splice plate 9 straddles the attachment zone 4 between the two panels 1, 2 at the level of the space made between the two vertical plates 18 and the vertical frame 5.
The prior art stringer splice plates 8, 9 have many drawbacks.
In particular, because of their single-piece structure and complex geometry, the prior art stringer splice plates are difficult to machine. The part has to be machined by arranging for several support surfaces, since one and the same piece is fixed to several elements with different orientations. These variations in the orientation of the fibers of the stringer splice plates generates major secondary bending moments which make it difficult to design and size these stringers and make said splice plates very sensitive to fatigue. Inasmuch as the stringer splice plates in particular have a function of transferring the longitudinal stresses induced by the bending of the panels to which they are fixed and provide them with continuity, they tend to rapidly suffer cracks at fatigue-critical sites. These fatigue-critical sites develop chiefly at the splice plate/stringer junctions and on the body of the stringer splice plate situated in the zone of attachment between the two panels. Furthermore, the fact of machining the stringer splice plates in the mass, i.e. out of a thick bar, causes said stringer splice plates to have weak mechanical characteristics. It is known that the characteristics of the materials deteriorates when the thicknesses of the semi-finished products increases.
The prior art orbital joining device, comprising a stringer splice plate 8,9 a sleeve 3 and a vertical frame 5 to join two stringers extending on adjacent panels has several drawbacks.
For example, should the vertical frame 5 be perforated to let through the body 12 of the stringer splice plate 8, the entire structure is penalized from the viewpoint of mass. During the sizing of the vertical frame 5, the designs made to achieve mechanical strength are done at the minimum height of the frame 5, i.e. in the upper part of said vertical frame 5 which is not crossed by the vertical notch 13 for passage of the stringer splice plate 8. Thus, all the matter of the vertical frame that is situated in the partial height h of the vertical frame 5, situated beneath the tip of said notch 13, is not taken into account for calculating mechanical strength. All this material is considered to be non-working. The vertical frame 5 is therefore over-sized. Thus, should the notch 13 extends over 27 mm of a height h, it is necessary to make a vertical frame 5 with a the total height of 90 mm to ensure at least 63 mm of working height. The term “total height ” is understood to mean the size of the frame 5 extending vertically from the base 14 to the peak of said frame 5.
Should the vertical frame 5 be clipped above the stringer splice plate 9, the presence of the additional sheeting elements 18 also tends to increase the mass of the fixation device as a whole.
It is an aim of the disclosed embodiments to provide a stringer splice plate that is of simple design, easy to manufacture and has high fatigue strength. It is another aim of the disclosed embodiments to provide an orbital joining device capable of at least partially resolving all or part of the problems explained here above.
To this end, the stringer splice plate of the disclosed embodiments is not a one-piece unit but, on the contrary, formed out of several independent parts, simple in shape and easy to make. The term “independent” is understood to mean physically and structurally independent as opposed to being made in one piece, i.e. they are not directly fixedly joined to one another and work independently of one another. More specifically, the stringer splice plate of the disclosed embodiments has at least three structurally independent elements each designed to be linked to different parts. Thus, a main element, designed to be fixed to the two adjacent stringers, only provides for the link between the two stringers. The link between each of said stringers and the structure to which they are fixed is provided by two other secondary elements which are also independent. Each of the two secondary elements of the stringer splice plate of the disclosed embodiments is, firstly, connected to only one of the two stringers and, secondly, to the structure along which said stringer extends. Each of the elements of the stringer splice plate works independently of the others, so as to separately take up the bending forces borne by the parts to which they are fixed. The stringer splice plate of the disclosed embodiments is simple to make since, by its geometry, each element is manufactured independently of the others. Each element has a limited number of support surfaces. Advantageously, each of said elements has a single support surface. The fatigue strength of the stringer splice plate of the disclosed embodiments is high because of the shape of the different elements that form it is not uneven and because of the separate absorption of bending or other forces. Furthermore, the stringer splice plate of the disclosed embodiments is easy to mount. Each of the elements of the stringer splice plate of the disclosed embodiments is designed to be connected to different parts, independently of the other two elements of the stringer splice plate. This provides for greater flexibility of assembly and especially enables compensation for any possible clearance between the two stringers that have to be fixedly joined to each other.
The orbital joining device of the disclosed embodiments, designed to fixedly join the two fuselage panels that face each other, perpendicularly to the longitudinal axis of said fuselage, comprises at least one stringer splice plate according to the disclosed embodiments, one vertical frame and one cross-piece extending transversely between the two panels to be fixedly joined. Thus, the fixing device of the disclosed embodiments has highly fatigue strength. Furthermore, since only the main element of the stringer splice plate, designed to connect two facing stringers longitudinally, must go through the vertical frame extending between the two panels, the notch for the passage of the stringer splice plate can be small in size. It is thus possible to reduce the section of the vertical frame considered as being a non-working part during the sizing of said vertical frame, thus providing especially for a major gain in mass.